[Vm-dev] VM Maker: VMMaker-dtl.350.mcz

[Eliot Miranda]

On Mon, Sep 8, 2014 at 2:43 PM, Tobias Pape <Das.Linux at gmx.de> wrote:

>
> Hi,
>
> On 08.09.2014, at 23:23, David T. Lewis <lewis at mail.msen.com> wrote:
>
> >
> > Hi Eliot,
> >
> > Agreed, the primitive will need to be rewritten to work with a 64-bit
> > SmallInteger. There may be other integer primitives that will need
> > attention too, although I have not looked.
> >
>
> Having tried implementing other SqueakVMs, my impression is, that the
> SmallInt-is-31-bit assumption is like everywhere. Starting with some
> int-primitives and not ending with bitBlt. We really have to be careful
> here.
>

That's what tests and sheer bloody-mindedness are for ;-)


>
> Best
>         -Tobias
>
> > Dave
> >
> >> Hi David,
> >>
> >> On Mon, Sep 8, 2014 at 12:18 PM, David T. Lewis <lewis at mail.msen.com>
> >> wrote:
> >>
> >>>
> >>> I know that "unsigned" means "unsigned int". That is the intent.
> >>>
> >>> With the primitive as currently implemented, that variable must be 32
> >>> bits, otherwise the shift left can successfully produce a five byte
> >>> large
> >>> integer that is truncated to four without failing the primitive. This
> >>> change is to fix the current implementation of the primitive in the
> case
> >>> of sizeof(sqInt) == 8.
> >>>
> >>
> >> OK, then it is fixing it in a way that will break a 64-bit
> implementation
> >> that uses 64-bit SmallIntegers.   Personally I find the method defective
> >> (for reasons already stated), and will be rewriting it soon.
> >>
> >>
> >>> Dave
> >>>
> >>>> Hi David,
> >>>>
> >>>>   and another issue is that "unsigned" is shorthand for "unsigned
> >>> int",
> >>>> so
> >>>> if you wanted to generalize the method to handle integers of the
> >>> system's
> >>>> word size (as is the case with 64-bit Spur which will have 61-bit
> >>>> SmallIntegers, unlike the 31-bit SmallIntegers in 64-bit Squeak) you'd
> >>>> want
> >>>> to use "usqInt", not "unsigned".
> >>>>
> >>>> On Sat, Sep 6, 2014 at 8:45 PM, <commits at source.squeak.org> wrote:
> >>>>
> >>>>>
> >>>>> David T. Lewis uploaded a new version of VMMaker to project VM Maker:
> >>>>> http://source.squeak.org/VMMaker/VMMaker-dtl.350.mcz
> >>>>>
> >>>>> ==================== Summary ====================
> >>>>>
> >>>>> Name: VMMaker-dtl.350
> >>>>> Author: dtl
> >>>>> Time: 6 September 2014, 11:44:28.389 pm
> >>>>> UUID: 2ad132b0-5fb3-4580-b5a8-29af12c3cb81
> >>>>> Ancestors: VMMaker-dtl.349
> >>>>>
> >>>>> VMMaker 4.13.6
> >>>>>
> >>>>> Fix primitiveBitShift (primitive 17) for sqInt declared 64 bits, as
> >>> in a
> >>>>> VM for 64-bit image format 68002.
> >>>>>
> >>>>> In image format 68002, bit shift left failed because of return type
> >>>>> limited to a 32-bit large integer, but internally the primitive
> >>>>> successfully shifted left into a variable declared as a 64 bit
> >>> sqInt..
> >>>>> The
> >>>>> simple fix (implemented here) is to declare the variable as 32 bit
> >>>>> unsigned
> >>>>> to agree with the 32-bit logic of the existing primitive.
> >>>>>
> >>>>> Note that permitting a left shift into a 64 bit variable makes sense
> >>>>> generally, and the primitive could be recoded to accomodate this for
> >>>>> shift
> >>>>> left, with the primitive answering positive64BitIntegerFor: rather
> >>> than
> >>>>> positive32BitIntegerFor: in the case of a shift left to allow for the
> >>>>> greater range (not implemented in this update).
> >>>>>
> >>>>> With this update, all KernelTests-Numbers tests pass for the 64-bit
> >>>>> image
> >>>>> format 68002.
> >>>>>
> >>>>> =============== Diff against VMMaker-dtl.349 ===============
> >>>>>
> >>>>> Item was changed:
> >>>>>  ----- Method: InterpreterPrimitives>>primitiveBitShift (in category
> >>>>> 'arithmetic integer primitives') -----
> >>>>>  primitiveBitShift
> >>>>>        | integerReceiver integerArgument shifted |
> >>>>> +       <var: #shifted type: 'unsigned'>
> >>>>> +
> >>>>>        integerArgument := self popInteger.
> >>>>>        integerReceiver := self popPos32BitInteger.
> >>>>>        self successful ifTrue: [
> >>>>>                integerArgument >= 0 ifTrue: [
> >>>>>                        "Left shift -- must fail if we lose bits
> >>> beyond
> >>>>> 32"
> >>>>>                        self success: integerArgument <= 31.
> >>>>>                        shifted := integerReceiver <<
> >>> integerArgument.
> >>>>>                        self success: (shifted >> integerArgument) =
> >>>>> integerReceiver.
> >>>>>                ] ifFalse: [
> >>>>>                        "Right shift -- OK to lose bits"
> >>>>>                        self success: integerArgument >= -31.
> >>>>>                        shifted := integerReceiver >> (0 -
> >>>>> integerArgument).
> >>>>>                ].
> >>>>>        ].
> >>>>>        self successful
> >>>>>                ifTrue: [self push: (self positive32BitIntegerFor:
> >>>>> shifted)]
> >>>>>                ifFalse: [self unPop: 2]!
> >>>>>
> >>>>> Item was changed:
> >>>>>  ----- Method: VMMaker class>>versionString (in category 'version
> >>>>> testing') -----
> >>>>>  versionString
> >>>>>
> >>>>>        "VMMaker versionString"
> >>>>>
> >>>>> +       ^'4.13.6'!
> >>>>> -       ^'4.13.7'!
> >>>>>
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>> best,
> >>>> Eliot
> >>>>
> >>>
> >>>
> >>>
> >>
> >>
> >> --
> >> best,
> >> Eliot
>
>
>
>


-- 
best,
Eliot
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